Influence of substrate temperature on In2S3 thin films synthesized via two-step sulfurization for ultra-sensitive and selective NO2 detection

In this article, we investigate In₂S₃ thin films deposited via a two-step sulfurization process, focusing on the impact of substrate temperature during indium deposition for its use in NO₂ detection. The films were prepared with indium deposited at 25°C, 200°C, and 300°C prior to sulfurization. X-ray Diffraction (XRD) analysis shows that all films form β-In₂S₃ in its tetragonal phase, with the film prepared by depositing indium at 300°C exhibiting a peak corresponding to cubic phase also. Composition analysis reveals variations in the indium-to- sulfur ratio among the films. Morphologically, the film prepared with depositing indium at 200°C displays petal-like structures, enhancing surface area. Photoluminescence (PL) analysis indicates higher concentration of defect levels in this film compared to other samples. X-ray Photoelectron Spectroscopy (XPS) shows the presence of oxygen on the surface of the samples. This oxygen presence was notably surface specific as it was not found deeper within the sample. Film synthesized with depositing indium at 200°C demonstrates promising application in sensing nitrogen dioxide (NO₂) gas at temperature comparatively lower than the reported values. The fabricated sensor made without using any dopants or heterostructures detected 800 ppb of NO₂ with a 12.25 % response. The sensor is also able to detect concentrations as low as 100 ppb.